1. Technical Field
The present invention relates to a radio transmitting apparatus and a radio transmission method.
2. Description of the Related Art
Mobile communication systems represented by a cellular communication system or wireless LAN (i.e., local area network) systems are provided with a random access region in their transmission regions. This random access region is provided in an uplink transmission region when a terminal station (hereinafter, “UE”) sends a connection request to a base station (hereinafter, “BS”) for the first time, or when a UE makes a new band allocation request in a centralized control system where a BS or the like allocates transmission times and transmission bands to UEs. The base station may be referred to as an “access point” or “Node B.”
Furthermore, in a system using TDMA (i.e., time division multiple access) such as the 3GPP RAN LTE, which is currently undergoing standardization, when a connection request is made for the first time (which takes place not only when a UE is powered on but also when uplink transmission timing synchronization is not established such as when handover is in progress, when communication is not carried out for a certain period of time, and when synchronization is lost due to channel conditions, and so on), random access is used for a first process of acquiring uplink transmission timing synchronization, connection request to a BS (i.e., association request) or band allocation request (i.e., resource request).
A random access burst (hereinafter, “RA burst”) transmitted in a random access region (hereinafter, “RA slot”), unlike other scheduled channels, results in reception errors and retransmission due to collision between signature sequences (situation in which a plurality of UEs transmit the same signature sequence using the same RA slot) or interference between signature sequences. Collision of RA bursts or the occurrence of reception errors increases processing delays in the acquisition of uplink transmission timing synchronization including RA bursts and processing of association request to the BS. For this reason, a reduction of the collision rate of signature sequences and improvement of detection characteristics of signature sequences are required.
As the method for improving the detection characteristics of signature sequences, generation of a signature sequence from a GCL (i.e., generalized chirp like) sequence having a low auto-correlation characteristic and also a low inter-sequence cross-correlation characteristic or Zadoff-Chu sequence is under study. A signal sequence, constituting a random access channel and known between transmission and reception, is referred to as a “preamble” and a preamble is generally comprised of a signal sequence having better auto-correlation and cross-correlation characteristics. Furthermore, a signature is one preamble pattern, and suppose the signature sequence and preamble pattern are synonymous here.
Furthermore, according to the technique described in Non-Patent Document 1, initial cell access including RA burst transmission is classified into processing started from the network side (BS side) and processing started from the UE side, the network side reports paging information including system information related to RA burst transmission to the UE through RA burst transmission and it is thereby intended to reduce the collision rate of signature sequences and improve detection characteristics.
To be more specific, paging information reported over a downlink includes uplink interference information (i.e., UL interference) and a dynamic persistent level parameter indicating retransmission time intervals or the like and the paging information is reported to each UE or a plurality of UEs using PCH (paging channel).
The UE having received the paging information uses the uplink interference information to set transmission power of RA bursts. Furthermore, since it is possible to control the error rate of RA burst transmission and RA burst transmission time intervals using the uplink interference information and dynamic persistent level parameter, priority of RA burst transmission can be controlled and the UE can select amore effective signature sequence.
In this way, detection characteristics of RACH improve in an access procedure started from the network side with the RACH system information transmitted through paging, whereas since RACH transmission is still contention based access, signature collision occurs.
In order to avoid signature collision, the access procedure started from the network side may allocate signatures and slots to be used for RACH transmission and may report the allocated signatures and slots to the UE through paging. The UE is set so as not to use the signature reported through paging for RACH transmission started from the UE side.    Non-Patent Document 1: R2-052769, LG Electronics, “Initial access for LTE” 3GPP TSG-RAN Working Group 2 #49 Seoul, Korea, Nov. 7-11, 2005